1. Field of the Invention
The present invention relates to a new and improved drilling fluid composition. More specifically, the present invention provides a new and improved well drilling and completion composition which when added to drilling mud prevents flocculation of drilled solids while simultaneously controls overall fluid rheology.
2. Description of the Prior Art
The value of potassium electrolytes for the inhibition of bentonite swelling in drilling fluids has been recognized since the late 1940's. It has been pointed out that potassium ions have a strengthening effect upon clay formations and that the potassium ions fit into the crystal structure of clay surfaces in such a manner as to not dissociate and create dispersive action among clay particles. The effectiveness of the potassium ion in limiting the peptization of clays has been shown and the effectiveness of potassium in combating the problems encountered while drilling through sensitive shale formations has been presented.
Although both potassium and sodium are alkali of similar atomic structure, their properties in colloidal systems have long been noted to be strikingly dissimilar. The majority of ions have an effective diameter much larger in water because of hydration and polorization effects; however, the monatonic ions of potassium, rubidium, and cesium are non-hydrated in water solution.
The potassium ion, the largest of the common ions in crystalline silicates does not change its volume when placed in solution and is therefore only one-third as voluminous as the sodium ion in solution. Inasmuch as adsorption is in inverse ratio to a power of the volume, the potassium ion is much more strongly absorbed on clays than is sodium. The sodium character of sea water in comparison with the potassium character of sedimentary rocks is due to this strong preferential adsorption of potassium by clays.
It is well known that under metamorphic conditions of temperature and pressure montmorillonite (bentonite) will be converted to illite if potassium is present. It has been shown, however, that this diagenetic modification can be initiated during the flocculation and settling of bentonitic sediments in sea water.
It is well documented in the literature that the potassium ion, because of its dimensional characteristics in solution will fit into the holes in the oxygen not of silicate surfaces. Because of this, it is attracted strongly to crystal lattice structure of clay surfaces and unlike the hydrated sodium ion, it is not free to dissociate and form a dispersive electrokinetic double layer. Adsorbed potassium ions thus act to inhibit the spontaneous dispersion of clays into water. It has been shown that the potassium ion is two (2) or three (3) times more effective in flocculating clay suspensions than it is the sodium ion.
The accumulation of evidence, including the fact that potassium ions are preferentially adsorbed by clays, even in the presence of sodium ions, establishes the potassium ion as a highly desirable cation to be employed in drilling fluid design to stabilize the bore hole.
It has been established that 3% to 5% of KCl solution (10 to 17 lbs./bbl.) must be maintained to control hydration and osmotic action in sensitive shale formation. A 15% KCl solution (50 lbs./bbl.) will inhibit the chemical dispersion of plastic bentonite masses and will convert calcium and sodium clays to potassium clays provided that a sufficient amount of time is allowed. However, the use of KCl is corrosive, costly and generally not reliably effective in normal drilling operations because there is not enough time for the conversion of the calcium and sodium clay to potassium clays.
U.S. Pat. No. 4,000,076 by Bodine, et al, teaches a phosphate added to a drilling mud containing potassium chloride to reduce corrosiveness. U.S. Pat. Nos. 3,079,334 and 3,079,335 to Clem discloses the use of water-soluble leonardite in combination with a water-soluble polyphosphate to provide drilling fluids of relatively low gel strength and viscosity which are effective in preventing hydration and swelling of native clays. Cates in U.S. Pat. No. 4,404,108 teaches reacting lignite and tannin together with sodium sulfite, paraformaldehyde and sodium hydroxide in water to give a reaction product suitable for use as a drilling fluid additive. U.S. Pat. No. 3,766,229 to Turner, et al, presents a dispersing agent and/or fluid loss control agent for drilling fluids obtained by employing sulfonated lignite and/or sulfonated humic acid wherein the cation for these salts are selected from alkali metals, alkaline earth metals and various elements having atomic numbers 57 through 71. U.S. Pat. No. 4,033,893 by Mondshine discloses a drilling fluid consisting essentially of a suspension of clay, lime, and a lignitic material in an aqueous phase.
What is needed and what has been invented is an improved, sodium free drilling fluid which prevents flocculation of drilled solids while simultaneously controlling overall fluid rheology. The standards of the mud systems for the past 30 years have been the dispersed mud systems comprising primarily lignosulfonates or lignite with a heavy metal, such as chrome or bichromates, to give these systems stability in controlling mud rheology. These systems have limitations of temperatures between 285.degree. F. and 300.degree. F. in controlling filtration and rheology simultaneously. In chemistry, this would be described as an electrochemical system.
The drilling fluid system of this invention is a deflocculating system, sodium free, allowing to control mud rheology and filtration simultaneously. Chemically, the improved system of this invention may be classed as a chemisorption process of a non-encapsulating polymer which functions as an uncoiled polymer and allows control of rheology and filtration without regard to calcium or chlorides levels or temperatures up to 500.degree. F. as long as the ingredients of the system are induced in accordance to the concentration of calcium and chloride or to the degree of temperature encountered while drilling the borehole to accommodate desired rheology relative to mud density and/or operators' demands and for filtration control desired.